Testing a thermodynamic approach to collective animal behavior in laboratory fish schools

Social animals including insects, fish, birds, and even humans exhibit self-organized collective behavior. Macroscopic properties arise not only from interactions between individuals, but also from environmental cues. Here, we present results from a series of experiments that utilize high speed footage of 2D schooling events, particle-tracking, and projected static and dynamic light fields to observe and control the behavior of negatively phototaxic laboratory fish schools (Hemigrammus bleheri). First, we use static light fields consisting of dark circular regions to produce visual stimuli that confine the schools to a range of areas. Next, we use dynamic light fields where the radius of the dark region shrinks linearly with time to compress the schools. Through measuring global quantities analogous to density, temperature, and pressure in statistical mechanics, we find that the temperature-like parameter depends on the speed of the compression. We discuss the implications of our results on current models.